Following injuries to Yohan Cabaye and Thiago Motta, Blanc has opted to move Luiz out of his normal defensive role and has been delighted with the Brazil international's performances.
The PSG coach insists he was always confident Luiz could adapt to a role further forward, having done so for former club Chelsea, and using him in midfield was not a last resort.
"It is not a question of a plan B," said Blanc. "He has helped us.
"We know he can play very well in this position, and it has allowed Cabaye and Thiago Motta to recover.
"[Adrien] Rabiot can play three positions but I think he [Luiz] is a better runner, and Marco [Verratti] in front of the defence lacks something."
Luiz is expected to continue in midfield on Wednesday as PSG meet Monaco in the quarter-finals of the Coupe de France three days after drawing 0-0 with the same opponents in Ligue 1.
"I hope it will be more lively, with goals," Blanc added. "I do not mind meeting again after a three-day interval.
"We hope some of our injured players will recover to play. The medical staff have been doing everything to get some players fit.
"We have important games ahead with a limited workforce."
